What are their motives:
To pump and dump.
Or
Pump and get the price of BTC and investors confidence up. In this instance I would hope the intentions are good!
No one can pump and dump bitcoin, in theory whales could do it if they are big enough but anyone will notice a huge movement of coins, so what we are seeing is just the natural movement of bitcoin in the market, get used to it because it is not going to change anytime soon.